The objectives of the proposed research are to: (1) develop models of limb hypertonia and hypotonia in experimental animals by placing lesions in the cerebellar nuclei, basal ganglia and cerebral cortex; (2) analyze the spinal sensory and motor apparatus with physiological techniques to determine the mechanisms underlying limb abnormalities of posture and tone; and (3) examine the compensatory changes following these lesions by analyzing nerve tissue regeneration in the central nervous system. The central nervous system lesions used to produce motor abnormalities are made with a cryogenic probe. The effects of the lesions on fusimotor activity are measured by recording the responses of Ia muscle spindle afferents to static and dynamic muscle extension. The effects on fusimotor activity of lesions in different structures are compared statistically to determine the interconnections and organization of these structures and their contribution to posture and muscle tone abnormalities. Regenerative changes in central nervous system neurons are being examined by measuring the neural activity of red nucleus cells following chronic partial and complete deafferentation. BIBLIOGRAPHIC REFERENCES: Copack, P.B., Felman, E., Lieberman, J.S., Gilman, S: Difference in proximal and distal condition velocities of efferent nerve fibers to the medial gastrocnemius muscle. Brain Res 91:147-150 (1975). Gilman, S: Patterns of motoneuron responses to natural stimuli, In Desiraju T (ed): Mechanisms in Transmission of Signals for Conscious Behavior. Chapter 2. Elsevier, Amsterdam 1976.